Life cycle assessment of agricultural residues utilization for biogas deployment

Production of biogas from energy crops, agricultural residues, and municipal waste is becoming increasingly important in order to reduce greenhouse gas (GHG) emissions and enhance the security of global energy supply. The environmental performance of biogas production from agricultural residues and its utilization as an alternative to fossil natural gas was evaluated and quantified in this study using a life cycle assessment (LCA) approach. The ‘cradle-to-grave’ LCA of a biogas production system was conducted in accordance with the ISO 14044 standards, using GaBi 4 computer software and life cycle inventory (LCI) data from the ecoinvent v2.0 database using the CML2001 method. The functional unit was the anaerobic digestion of 1 ton of agricultural residue mixture to produce biogas with the digestate as a process co-product. The environmental profile was analysed in terms of abiotic depletion potential (ADP), acidification potential (AP), eutrophication potential (EP), global warming potential (GWP), ozone layer depletion potential (ODP), human toxicity potential (HTP), photochemical ozone creation (POCP), freshwater aquatic ecotoxicity potential (FAETP), and terrestrial ecotoxicity potential (TETP). Results showed that using biogas as a replacement for natural gas can directly help in offsetting the environmental impacts associated with the production and use of fossil natural gas – ADP (-44.93 kg Sb-Equiv.); AP (-16.99 kg SO2-Equiv.); EP (-1.93 kg Phosphate-Equiv.); GWP (-10329.4 kg CO2-Equiv.); ODP (-0.0007 kg R11-Equiv.); HTP (-2695.38 kg DCB-Equiv.); POCP (-1.44 kg Ethene-Equiv.); FAETP (-73.0778 kg DCB-Equiv.); and TETP (-55.58 kg DCB-Equiv.). Using biogas obtained through anaerobic digestion of agricultural crops such as corn stover and rice straw can be very beneficial when compared to fossil natural gas derived energy.